As fine circuit lines are high-densely integrated in a semiconductor device, precise polishing corresponding thereto needs to be performed on the surface of a wafer. In order to more precisely perform polishing of a wafer, a mechanical polishing process and Chemical Mechanical Polishing (CMP) process in which mechanical polishing and chemical polishing are combined may be performed.
The CMP process is a process of precisely polishing the surface of a water for the purpose of the global planarization for removing a height difference between a cell region and a surrounding circuit region due to an unevenness of the wafer surface generated when masking, etching and interconnection processes of a semiconductor device manufacturing process are repeatedly performed, and the improvement of wafer surface roughness due to high integration of a device and separation contact/wiring film for forming a circuit.
In the CMP process, a wafer is pressurized while a process surface of the wafer faces a polishing pad, and thus chemical polishing and mechanical polishing of the process surface are simultaneously performed. The wafer on which the polishing process is performed is gripped by a carrier head, and then goes through a cleaning process for removing foreign substances from the process surface.
As shown in FIG. 1, when a wafer (W) is supplied to a chemical mechanical polishing system (X1) from a loading unit (20), the chemical mechanical polishing process is performed on a plurality of polishing surface plates (P1, P2, P1′, and P2′) while the wafer (W) is moved (66-68) along a predetermined path (Po) in a state where the wafer (W) is adhered closely to carrier heads (S1, S2, S1′, and S2′; S). The wafer (W) on which the chemical mechanical polishing process is performed is transferred to a cradle (10) of an unloading unit by the carrier head (S), and then is transferred to a cleaning unit (X2) where a cleaning process is performed. Thereafter, a process of removing foreign substances from the wafer (W) is performed in a plurality of cleaning modules (70).
However, since the time taken for the polishing process that is performed in each polishing surface plate is different from the time taken for the cleaning process in each cleaning unit (C1, C2), the wafer (W) transferred by the carrier head (S) may not be introduced into a next process immediately after one process is finished, thereby causing a process delay.
Meanwhile, as a semiconductor is further miniaturized and highly integrated, the importance of the cleaning efficiency of a wafer is growing more and more. Particularly, when foreign substances remain on the surface of a wafer even after the cleaning process of a wafer is finished in the cleaning module, the yield may be reduced, and the stability and reliability may be reduced. Accordingly, foreign substances need to be removed in the cleaning module to the maximum.
For this, there has been proposed a method of increasing the cleaning efficiency, by preparatorily cleaning a wafer to remove foreign substances before a wafer having undergone the polishing process is transferred to the cleaning module and then by again cleaning the wafer in the cleaning module.
However, this method has a limitation in that since a preliminary cleaning space needs to be additionally prepared to perform a separate preliminary cleaning independently of the cleaning module, the layout of equipment is disadvantageous and the transfer and cleaning treatment process of the wafer becomes complicated. Also, the cleaning time increases, and the cost increases but the yield decreases. Particularly, since a wafer unloaded to an unloading position after the polishing process needs to go through a complicated process of being transferred to the separate preliminary cleaning space for the preliminary cleaning and then being again transferred to the cleaning module, the whole treatment process efficiency of a wafer is reduced.
Accordingly, various studies for improving the cleaning efficiency and the yield and reducing the cost are being conducted, but are still insufficient and more development related thereto is needed.